1. Field of the Invention
The present invention relates to a resonator and to a filter, which are small in size and suitable for wireless communication devices such as a cellular telephone.
2. Description of the Related Art
There has been a demand for a reduction in size of a filter used in wireless communication devices such as a cellular telephone, and the reduction in size has accordingly been demanded also for resonators structuring the filter. To achieve the reduction in size, a filter which utilizes a TEM (Transverse Electro-Magnetic) line to structure the resonator has been developed. In general, a comb-line coupling and an interdigital coupling are two techniques for coupling the two resonators having the TEM line. Japanese Patent Application Unexamined Publication No. 2003-218604 discloses a stacked resonator utilizing the comb-line coupling. Japanese Patent Registration No. 4195036 discloses a stacked resonator utilizing the interdigital coupling.